Page 458 - Veterinary Toxicology, Basic and Clinical Principles, 3rd Edition

VetBooks.ir Chapter 26

Copper

Larry J. Thompson

INTRODUCTION Each of these may have a different clinical presenta-
tion, with the main target organs for acute copper expo-
Copper is a transition group metal with high electrical
sure generally being the gastrointestinal (GI) tract, liver,
and thermal conductivity. The chemical abbreviation
and kidney, with the target organs for chronic problems
for copper is Cu, which comes from the Latin word
being the liver, red blood cells, and kidney.
cuprum, which refers to the island of Cyprus, known
Dietary sources of copper include normal plant con-
in the ancient times for large deposits of copper ore.
centrations of copper, with forages and cereal grains usu-
The Bronze Age followed the discovery that adding ally containing less than 10 ppm copper on a dry matter
tin (and other metals) to copper made the resulting
(DM) basis. Some oilseed meals can contain up to
metal alloy much more durable. Copper has been
35 ppm copper in DM. By far the largest source of copper
shown to be an essential element for both animals and
in the diet will be feed additives such as copper sulfate,
plants but can be toxic under certain conditions. This
copper chloride, and copper oxide. Additional sources of
chapter describes the toxicity and deficiency of copper
copper for the animal may be chelated copper sources in
in animals.
the diet or the administration of boluses containing copper
metal wires or other solid forms of copper that remain in
the rumen/reticulum and slowly dissolve over time.
BACKGROUND Misformulation of rations or errors in the mixing of feed
can result in high concentrations of copper. Problems can
Toxic insults from copper occur in two main categories,
arise from the use of feed formulated for a copper-
acute and chronic. The acute overexposure of animals to
tolerant species when used for a copper-sensitive species
copper can occur by both oral and parenteral routes
such as sheep, or the use of trace mineralized salt in sheep
(Galey et al., 1991) but is relatively uncommon. Sheep
diets. Other sources for large acute oral copper exposures
are very susceptible to chronic copper poisoning, where
would include copper sulfate foot baths and copper algae-
even a slight excess of copper in the diet can build
cides or fungicides. Most water sources have low copper
up over weeks or months to cause problems. Cattle and
concentrations but the use of copper piping with slightly
other ruminants are less likely to suffer from chronic
acidic water can result in additional copper being
mild to moderate copper excesses in the diet but can be
dissolved.
affected by relatively high levels (Gummow, 1996;
Engle, 2014). Monogastric animals seem to tolerate
excess dietary copper much better than ruminants PHARMACOKINETICS
and high dietary copper additions (up to 250 ppm) have
been used for growth promotant effects, such as in pigs Copper is primarily absorbed in the small intestine and
and poultry. Finally, certain breeds of dogs (e.g., transported in the blood by transcuprein and albumin,
Bedlington terriers) have a genetic predisposition for which serve to reduce the oxidative effects of divalent
liver copper accumulation similar to Wilson’s disease in copper. In the liver, copper can be stored in the lyso-
humans (Taboada and Thompson, 1997). Genetic somes, excreted in the bile or incorporated into cerulo-
characterization of Labrador Retrievers has shown plasmin for use and transport to cells in other parts of the
other genes and expression patterns may represent a body. Biliary excretion is the major mechanism responsi-
new model for copper metabolism disorders (Fieten ble for copper homeostasis and identified genetic disor-
et al., 2016; Wu et al., 2016; Dirksen et al., 2017). ders of copper accumulation are due to impaired biliary
Veterinary Toxicology. DOI: http://dx.doi.org/10.1016/B978-0-12-811410-0.00026-X
Copyright © 2018 Elsevier Inc. All rights reserved. 425